This problem can be reproduced using netperf and netserver.

On server:
smc_run netserver

On client:
smc_run netperf -H 127.0.0.1 -l 1
[]# smc_run netperf -H 127.0.0.1 -l 1
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) ...
Recv   Send    Send
Socket ...     Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

131072 131072 131072    0.00     1723.79

This is because netperf obtains the smc sndbuf size as 131072 
through getsockopt. It calls sendmsg to send 131072 bytes of 
data at a time, but smc actually returns after only sending 
65504 bytes (65536 - sizeof(cdc head)), and then netperf 
terminates the test.

In smc_tx_sendmsg, the processing after the sending ring buf 
is full is to return directly, so the above phenomenon is caused.

I would like to ask if here after the sending ring buf is full, 
enter smc_tx_wait and wait for the peer to read before continuing 
to send.

When I delete the judgment of send_done in front of smc_tx_wait, 
it seems to work normally:

[]# smc_run netperf -H 127.0.0.1 -l 1
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) ...
Recv   Send    Send
Socket ...     Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

131072 131072 131072    1.00     11543.80

liqiang (1):
  Enter smc_tx_wait when the tx length exceeds the available space

 net/smc/smc_tx.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

-- 
2.43.0